Friday, November 17, 2006


Opiorphin--natural painkiller

A natural painkiller more powerful than morphine has been discovered in human saliva, and may lead to improvements in the clinical treatment of pain, French scientists say.

The compound, called opiorphin, acts on pathways involving not just pain, but also emotional responses, according to the researchers.

"Our discovery of opiorphin is extremely exciting from a physiological point of view," they wrote in a paper published today in the U.S. journal Proceedings of the National Academy of Sciences.

They are hopeful that new insights into the body's natural response to pain will lead to improvements in its pharmaceutical treatment.

The research team, led by Catherine Rougeot from the Institut Pasteur in Paris, France, had previously identified a potent inhibitor of pain in rats called sialorphin, and wondered whether humans might secrete a similar compound.

Their suspicions were confirmed when they isolated the human relative of sialorphin from saliva, naming it opiorphin. They then compared opiorphin's pain killing power with the widely used opiate morphine, using a number of tests of pain in rats.

The typical amount of opiorphin used in the tests was one milligram per kilogram of body weight - far more than the human body naturally produces in saliva. However not only was opiorphin just as effective as morphine as a painkiller, it was also active at much lower concentrations.

In one test, researchers injected a pain-inducing chemical called formalin into the paws of rats. The amount of time rats spent shivering and licking their paws, which are common indicators of pain, was significantly reduced when opiorphin was administered.

In another experiment rats were exposed to a mini-bed of nails. Those who had been given opiorphin were brave enough to spend more time walking on the tiny steel pins than rats who hadn't been given any painkiller.

"Because of its properties, opiorphin may have therapeutic implications," the researchers said. They think opiorphin could be used directly as a painkiller, or could provide a template for the design of more powerful drugs.

Next, the authors hope to identify which physiological conditions trigger the release of opiorphin. They suspect that fearful or stressful situations might be the key, since these kinds of scenarios lead to the production of opiorphin's equivalent in rats.

But the applications of opiorphin could go far beyond pain and stress relief. Rougeot and colleagues also foresee its use in the treatment of mood-related disorders, since it has been found to act in biological pathways underlying anxiety, aggression, emotional and motivational responses.

According to the researchers, preliminary studies have shown opiorphin to have antidepressant activity, and it might just be a new weapon in the battle against male erectile dysfunction.

The researchers report that three different models of erectile dysfunction have been created in rats, based on common causes in men: diabetes, age-related and neurological impotence. In all three cases, the rat equivalent of opiorphin was found to be decreased in production.

Questions of treatment aside, the French team point out that opiorphin could be a useful marker for the identification of erectile dysfunction.

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